The process of booting a computer often involves starting dozens if not hundreds of individual services and applications. Virtually all of the services and applications access data stored in nonvolatile memory, such as a disk drive. As each of the services and applications being started requests its associated data, the nonvolatile memory, particularly a disk drive, becomes input-output bound and cannot service the requests at the rate the requests arrive. Those familiar with computers, especially personal computers, may have noted the indicator light associated with disk activity remains on almost continuously during a boot cycle. This is evidence of the boot process being disk I/O bound. The result is lengthy boot times that only increase as more services are added, causing increasing frustration on the part of a user waiting to use the computer.
One attempt at improving boot time monitored disk access at a high level to create a log of logical file accesses, that is, files by name that were used in the boot process. These files were loaded at boot time and cached for retrieval by a foreground process that may subsequently request information contained in the file. However, this technique provided only limited improvement because entire files were retrieved, potentially from different areas of the disk, when only a portion of the file might be required. Further, no consideration was given to the physical location of the file on the desk. Retrieving more data than was required, particularly in light of the potential increase in disk access time, placed a limit on an overall reduction in boot time.